EP0325494B1

EP0325494B1 - Seals

Info

Publication number: EP0325494B1
Application number: EP89300593A
Authority: EP
Inventors: Gavin Stuart Oseman
Original assignee: Dowty Seals Ltd
Current assignee: Dowty Seals Ltd
Priority date: 1988-01-21
Filing date: 1989-01-23
Publication date: 1992-08-26
Anticipated expiration: 2009-01-23
Also published as: GB8801359D0; DE68902546D1; DK24289D0; EP0325494A1; DK24289A; DE68902546T2; JPH01220775A; US5088744A; DK168457B1

Description

Technical Field

This invention relates to seals and, more particularly, to sealing assemblies for use between two components which are movable relative to each other, especially reciprocating components such as pistons or rods contained within a housing.
Sealing assemblies are known which comprise, in cross-section, a generally 'T'-shaped element of elastomeric material and two supporting elements positioned on either side of the vertical portion of the 'T' and bounded by the "top" of the 'T' (i.e. the horizontal portion from which the vertical portion depends centrally) and being of non-resilient, i.e. in use non-extrudable, material.
Such an assembly is commonly annular in overall shape and operates by its placement in a groove in one of the components to be sealed with the remote end of the vertical portion of the 'T' protruding as a sealing lip and by the non-resilient material preventing, in use, its extrusion between the moving components. As such, these assemblies have generally been superior to conventional 'O'-rings and similar seals.
The known assemblies of this type have been provided with a sealing lip of semi-circular cross-section (measured in the free condition) so that the surface of the other component to be sealed is arranged tangentally relative to the sealing lip. Such an assembly is disclosed in FR-A-2604235.

Disclosure of the Invention

Although the known assemblies of this type have been employed widely, it has now been surprisingly found that their sealing characteristics can be improved by providing the sealing lip in particular with a different shape.
In accordance with the invention there is provided an annular sealing assembly which comprises a resilient sealing element having a T-shaped cross section having an axially extending portion and a radially extending portion that extends radially from the axially extending portion and has opposed sides and a rounded sealing lip at an end remote from the axially extending portion which meets said opposed sides at turning points, the assembly also comprising supporting elements of substantially non-resilient material positioned one adjacent each of said opposed sides of the radially extending portion, characterised in that the surface of the rounded sealing lip between the turning points is substantially elliptical in form when the sealing element is undeformed.
In preferred assemblies, the surface of the rounded sealing lip projects radially from said turning points a distance 15 to 40% of the axial distance between said turning points, and lies within a pair of semi-ellipses which respectively project radially from said turning points a distance of 15 and 40% of the distance therebetween.
Most preferably the surface of the rounded sealing lip between the turning points projects radially from said turning points a distance of less than about 30% of the axial distance between said turning points, and advantageously it projects radially 15 to 25% of the axial distance between said turning points.
The surface of the rounded sealing lip between the turning points is substantially elliptical in form when the seal is undeformed. The expression "substantially elliptical in form" is used herein to mean a curved shape which lies on or approximates to an ellipse and which may be composed of a plurality of circular arcs, but which is not a single circular arc. The junction between the radially extending portion and the axially extending portion is preferably radiussed in order to maintain the integrity of the sealing element over a prolonged period of time.
It is when this radiussing is substantial that it may extend as far as the beginning of the sealing lip; in such cases, the radially extending portion does not possess parallel sides and there is simply a turning point between the radiussing and the lip.
Whatever are the dimensions of the sealing element, the complementary elements will generally be of corresponding shape so that they will closely fit the sealing element. However, they will generally not follow the arcuate shape of the sealing lip because, in use, the elastomeric lip is designed to be urged into the gaps formed between the lip and the respective complementary elements.
The sealing element may be made from any suitable elastomeric material such as neoprene or any natural or synthetic rubbers.
The complementary elements, on the other hand, must be made from substantially non-elastomeric substances such as PTFE, Nylon or any suitable plastic composition. Although not preferred, metallic supporting elements may be employed.

Description of the Drawings

For a better understanding of the invention, reference is now made by way of exemplification only to the accompanying drawings in which:

Figure 1 shows a cross-section through a sealing assembly of the invention, and
Figure 2 shows a cross-section through a further sealing assembly of the invention.

Best Mode of Carrying out the Invention

With reference to Figure 1, there is shown in cross-section a sealing assembly of the invention which comprises a substantially T-shaped element 1 having (in the view shown in this drawing) an axially extending portion 2 from which depends perpendicularly and centrally a radially extending portion 3. The element 1 as a whole is of annular shape with the radially extending portion innermost (although in other embodiments it could be outermost) and is made from elastomeric material. At the end of the radially extending portion 3 remote from the axially extending portion 2 there is a sealing lip 4 which is substantially elliptical in shape.
There is radiussing R of the angle between the axially exending portion and the radially extending portion of the element 1 but the sides of the radially extending portion 3 are parallel between this radiussing and the sealing lip 4, the lip being defined herein as beginning at the point P where the sides of radially extending portion 3 cease to be parallel. The major radius A is measured at the point P and the minor radius B measured centrally between major radii A and the end of the sealing lip 4 remote from the axially extending portion 2. In this embodiment the minor radius B is 50% of the major radius A.
Supporting elements 5, 6 having a shape complementary to that of the T-shaped element 1 in the vicinity of the radiussing R and parallel sides of the element 1 in particular (but not in the vicinity of the sealing lip 4) are located on either side of the element 1. The supporting elements 5, 6 are made from a substantially non-elastomeric substance, in this case PTFE, and are not joined to the T-shaped element 1.
Prior to use, the assembly is placed in a groove (or whatever) in one of the two components to be sealed with the sealing lip 4 proud of the edges 7, 8 of the supporting elements 5, 6 respectively, i.e. as shown in Figure 1. The measurement of the major and minor radii are measured in this state, i.e. in the free condition of the element 1. In actual use of the sealing assembly, the lip 4 will therefore engage with the other component and the lip 4 brought into line with the edges 7, 8. Relative movement between the respective components, and/or pressure energisation, will cause distortion of the lip and its displacement into the gaps 9, 10 formed between the sealing lip 4 and the supporting elements 5, 6. The surfaces 7, 8 remain in firm engagement with the other component and prevent extrusion of the elastomeric material of the lip 4 into any gap which might otherwise exist between the respective components.
The sealing assembly shown in Figure 2 works on the same principle as that of Figure 1. However, the radially extending portion of the T-shaped element does not have parallel sides and the radiussing between the axially extending portion and the radially extending portion of the T-shaped element extends up to that part of the radially extending portion defining the sealing lip. There is therefore a turning point T where the sealing lip begins and the major and minor radii are measured with reference to the point T. In this case the minor radius is 75% of the major radius.

Claims

An annular sealing assembly which comprises a resilient sealing element (1) having a T-shaped cross section having an axially extending portion (2) and a radially extending portion (3) that extends radially from the axially extending portion (2) and has opposed sides and a rounded sealing lip (4) at an end remote from the axially extending portion (2) which meets said opposed sides at turning points (T, P), the assembly also comprising supporting elements (5) of substantially non-resilient material positioned one adjacent each of said opposed sides of the radially extending portion (3), characterised in that the surface of the rounded sealing lip (4) between the turning points (T, P) is substantially elliptical in form when the sealing element (1) is undeformed.
A sealing assembly as claimed in claim 1 further characterised in that the surface of the sealing lip (4) projects radially from said turning points (T, P) a distance 15 to 40% of the axial distance between said turning points.
A sealing assembly as claimed in claim 1 or 2 further characterised in that the surface of the rounded sealing lip (4) between the turning points (T, P) lies within semi-ellipses, one of which projects radially from said turning points a distance 15% of the axial distance between said turning points, and the other of which projects radially from said turning points a distance 40% of the axial distance between said turning points when the sealing element (1) is undeformed.
A sealing assembly as claimed in claim 3 further characterised in that the surface of the rounded sealing lip (4) between the turning points (T, P) projects radially from said turning points a distance of less than about 30% of the axial distance between said turning points.
A sealing assembly as claimed in claim 4 further characterised in that the surface of the rounded sealing lip (4) between the turning points (T, P) projects radially from said turning points a distance between about 15 to 25% of the axial distance between said turning points.
A sealing assembly as claimed in any one of the preceding claims further characterised in that the surface of the sealing lip (4) is symmetrical about the centre line of the cross-section of the radially extending portion (3).
A sealing assembly as claimed in claim 5 further characterised in that the surface of the sealing lip (4) is semi-ellipsoidal.
A sealing assembly as claimed in any one of the preceding claims further characterised in that junctions (R) between the opposed sides of the radially extending portion (3) and the axially extending portion (2) are radiussed.
A sealing assembly as claimed in any one of the preceding claims further characterised in that the supporting elements (5) are shaped in a complementary manner to the adjacent surfaces of the sealing element (1) so that they are a close fit therewith but are spaced away from the surface of the sealing lip (4).